This application is based on Japanese Patent Application No. 2009-059919 filed with the Japan Patent Office on Mar. 12, 2009, the entire content of which is hereby incorporated by reference.
1. Technical Field
The present invention relates to a three-dimensional vision sensor for recognizing a target object through three-dimensional measurement processing using a stereo camera.
2. Related Art
In order to perform three-dimensional measurement using a stereo camera, it is necessary to determine a perspective transformation matrix P (refer to the following equations (1) and (2)) in a transformation equation indicative of a relationship between a world coordinate system and a coordinate system of each camera constituting the stereo camera.
                    (                  Equation          ⁢                                          ⁢          1                )                                                                      λ          ⁡                      [                                                            x                                                                              y                                                                              1                                                      ]                          =                  P          ⁡                      [                                                            X                                                                              Y                                                                              Z                                                                              1                                                      ]                                              (        1        )                                (                  Equation          ⁢                                          ⁢          2                )                                                            P        =                  [                                                                      P                  00                                                                              P                  01                                                                              P                  02                                                                              P                  03                                                                                                      P                  10                                                                              P                  11                                                                              P                  12                                                                              P                  13                                                                                                      P                  20                                                                              P                  21                                                                              P                  22                                                                              P                  23                                                              ]                                    (        2        )            
The respective components P00, P01, . . . P23 in the perspective transformation matrix P reflect internal parameters of the camera (a focal length, a resolution, an image center and the like) and parameters induced by a position and an attitude of the camera (a rotational deviation of the camera coordinate system with respect to the world coordinate system, an amount of positional deviation between origin points in the respective coordinate systems, and the like). Conventional calibration processing has acquired, for each camera, plural sets of two dimensional coordinates (x, y) and three-dimensional coordinates (X, Y, Z) in the coordinate system of the camera, further substitutes each set of coordinates into the equation (1) to define multiple simultaneous equations having the respective components in the matrix P as unknown numerical values. Further, most preferable values of the respective components are specified according to a least square method.
Next, as documents which disclose methods for easily deriving the coordinates for use in the aforementioned calculations, there are Zhengyou Zhang “A Flexible New Technique for Camera Calibration”, Microsoft Research Microsoft Corporation, [searched in Feb. 2, 2009], the Internet <URL: http://research.microsoft.com/en-us/um/people/zhang/calib/> and JP-A No. 2006-250889 to which Zhengyou Zhang “A Flexible New Technique for Camera Calibration” is applied. Zhengyou Zhang “A Flexible New Technique for Camera Calibration”, Microsoft Research Microsoft Corporation, [searched in Feb. 2, 2009], the Internet <URL: http://research.microsoft.com/en-us/um/people/zhang/calib/> describes performing at least two image pickups on a flat-plate-shaped work provided with a two-dimensional calibration pattern configured by marks arranged at equal intervals while changing the height and the orientation of the work, then extracting characteristic points corresponding to the respective marks from the images created by the respective image pickups and, further, specifying coordinates in the world coordinate system from the relationship among the characteristic points.
Further, JP-A No. 2006-250889 describes performing an image pickup at a state where two transparent sheets provided with different calibration patterns are placed horizontally with a predetermined interval interposed therebetween, in order to enable acquiring a number of characteristic points required for the calibration patterns from the same image, and further setting the Z coordinate (the coordinate indicative of the height) of a plane coincident with the lower transparent sheet to zero, in order to calculate parameters.